docs: def stream_length(self):
          """Returns the length of the source stream, determining it if not already known."""
          if self._stream_length is None:
              try:
                  current_position = self.source_stream.tell()
                  self.source_stream.seek(0, 2)
                  self._stream_length = self.source_stream.tell()
                  self.source_stream.seek(current_position, 0)
              except Exception as error:
                  # Catch-all for unknown issues encountered trying to seek for stream length
                  raise NotSupportedError(error)
          return self._stream_length